This invention relates generally to fluid flow meters, and more particularly to flow meters of a type having a paddle wheel rotatably mounted within a substantially cylindrical cavity.
An example of a fluid flow meter of this particular type is described in U.S. Pat. No. 4,173,144 to Edwin Pounder. It includes a paddle wheel mounted for rotation in a cylindrical cavity, and inlet and outlet conduits for directing a fluid to flow through the cavity and rotate the paddle wheel at an angular velocity corresponding generally to the flow rate. The paddle wheel rotates about an axis aligned with the cavity's longitudinal axis, and a special optical sensor senses its angular velocity to provide a signal indicative of the fluid flow rate.
Although flow meters like the one described above have generally performed satisfactorily, especially at relatively high flow rates, they are believed to be limited in the range of Reynolds numbers over which they can operate effectively. The devices are generally effective when measuring flows having relatively high Reynolds numbers, i.e., turbulent flow, but are generally ineffective for flows having relatively low Reynolds numbers, i.e., laminar flow. This can be a drawback in flow meter applications such as soft drink dispensers, where the viscosity of the fluids being dispensed can vary significantly and the flow can be either laminar or turbulent.
It should therefore be appreciated that there is a need for an improved paddle wheel type flow meter that can operate effectively for fluid flows covering an extended range of Reynolds numbers. There is particularly a need for a flow meter that can operate effectively for a range of Reynolds numbers spanning both turbulent and laminar flow regimes. The present invention fulfills this need.